1. Technical Field
The present invention relates to an organic electroluminescent display device and, more particularly, to an organic electroluminescent display device having a pixel circuit which allows a main display panel and a sub display panel to share a data line and a power supply voltage line.
2. Related Art
An electroluminescent display device (hereinafter referred to an EL display device) is an emissive device in which a fluorescent material emits light when electrons and holes recombine to thereby display an image. EL display devices are classified into inorganic EL display devices which use an inorganic compound as the fluorescent material and organic EL display devices which use an organic compound as the fluorescent material. EL display devices have many advantages, such as low driving voltage, self-emission, thin film characteristics, wide viewing angle, fast response speed, high contrast, and so forth. Thus, EL display devices are expected to take center stage among the next generation of display devices. Among EL display devices, an organic EL display device can display an image having a high luminance of tens of thousands of [cd/m2] with a voltage of about 10V. Thus, most EL display devices coming into widespread use are organic EL display devices.
Methods of driving an organic EL display device may be classified into passive matrix type methods and active matrix type methods which use a thin film transistor (TFT). The passive matrix type method has an anode electrode (i.e., indium-tin-oxide; ITO) and a cathode electrode (metal) arranged orthogonally, and selects an associated line for driving. The active matrix type method connects the TFT and a capacitor to respective pixel electrodes so as to maintain a voltage using the capacitance of the capacitor. Among these types, when the organic EL display device is driven by the passive matrix type driving method, a high instantaneous luminance is required. This consumes a large amount of power and reduces the lifespan of the organic light emitting diode. As a result, almost all recently manufactured organic EL display devices are driven by the active matrix type driving method. Such an active matrix type organic EL display device (AMOLED) is applied to various devices, including cellular phones, personal digital assistants (PDAs), electronic dictionaries, and so forth.
In particular, a dual emission organic EL display device, which has a main display panel and a sub display panel in one, is increasing in use. The main display panel and the sub display panel have different sizes and display different images. For example, in a folder type cellular phone, an inner window for displaying main images (picture, background, characters, menu, etc.) when the folder is opened is the main display panel, and an outer window for displaying simpler images (time, date, etc.) when the folder is closed is the sub display panel.